The entire disclosure of Japanese Patent Application No. 2005-315137, filed on Oct., 28, 2005, and Japanese Patent Application No. 2006-276855, filed on Oct., 10, 2006, is expressly incorporated by reference herein.
1. Technical Field
The present invention relates to a method for forming a mark and a liquid ejection apparatus.
2. Related Art
Normally, an electro-optic apparatus such as a liquid crystal display or an electroluminescence display includes a substrate that displays an image. The substrate has an identification code (for example, a two-dimensional code) including product information regarding the name of the manufacturer and the product number, for purposes of quality control and production control. The identification code includes a plurality of dots formed by, for example, colored thin films or recesses. The dots are arranged in a predetermined pattern so that the identification code can be identified in accordance with the arrangement pattern of the dots.
As a method for forming an identification code, JP-A-11-77340 discloses a laser sputtering method and JP-A-2003-127537 discloses a waterjet method. In the laser sputtering method, a code pattern is formed through sputtering by radiating a laser beam onto a metal foil. In the waterjet method, dots are marked on a substrate by ejecting water containing abrasive onto the substrate.
However, in the laser sputtering method, the interval between the metal foil and the substrate must be adjusted to several micrometers to several tens of micrometers in order to form each dot in a desired size. The substrate and the metal foil thus must have extremely flat surfaces and adjustment of the interval between the substrate and the metal foil must be carried out with accuracy on the order of micrometers. This limits application of the method to a restricted range of substrates, and the use of the method is limited. In the waterjet method, the substrate may be contaminated by water, dust, and the abrasive that are splashed when the identification code is formed.
In order to solve these problems, an inkjet method has been focused on as an alternative method for forming an identification code. In the inkjet method, dots are provided on a substrate by ejecting droplets of liquid containing metal particles from nozzles of an ejection head onto the substrate. The droplets are then dried to provide the dots. The method thus can be applied to a relatively wide range of substrate materials. Further, the method prevents contamination of the substrate caused by formation of the identification code.
In most of cases where the inkjet method is employed, the composition (for example, the metal particles or dispersion medium) of the liquid to be ejected or the size of a droplet must be changed in correspondence with the type of the dots or the surface condition of the substrate. Therefore, if drying of the droplets can be carried out in correspondence with the composition of the liquid and the size of the droplet in the drying process, formation of a pattern by the dots obtained from the droplets is facilitated. Further, the inkjet method becomes applicable to a wider range of use.
As one such droplet drying method, for example, a laser beam with an alterable radiation angle may be radiated onto a zone on the substrate corresponding to each of the droplets, thus irradiating the droplet with the laser beam. This instantly solidifies the target droplet. The optical cross section and the energy density of the laser beam are thus changed in correspondence with the type of the liquid forming the droplets and the size of each droplet.
Specifically, if the radiation angle of the laser beam radiated onto each droplet is altered, that is, if the position of a laser head that radiates the laser beam is changed, the radiating position of the laser beam changes correspondingly. Therefore, the radiating position of the laser beam must be corrected in correspondence with changes to the liquid forming the droplets or the size of each droplet. This consumes time and may lower productivity for forming code patterns.